1. Field of the Invention
The present invention relates to automatic slack adjuster arrangements for vehicle brakes and, more generally, to any sort of arrangement that requires the use of a saw-tooth clutch having a high resolution. By way of the invention, problems relating to a stabilized stroke value being too large in an automatic slack adjuster using a saw-toothed one-way clutch are addressed.
2. Description of Related Art
Saw-toothed one-way clutches are often used in automatic slack adjusters. During one part of a braking cycle, i.e. during brake application or brake return, an input side of such a one-way clutch slips past an output side by an angle proportional to the increase in stroke due to brake wear. During the other part of the cycle, the input side of the one-way clutch engages with teeth at the output side to drive the one-way clutch output side. The output side of the one-way clutch turns a worm-shaft, which turns a worm gear coupled to a shaft of the brake cam shaft to compensate for lining wear.
Conventional devices typically have fixed teeth on the input and output sides and hence resolution is limited by the number of teeth that can be incorporated into mating clutch parts. Some automatic slack adjusters, of course, use wrap spring clutches, which employ close wound helical springs made from wire with a square cross-section. These clutches are stepless, which means they deliver outputs in response to very small inputs. A saw-toothed one-way clutch, by contrast, will deliver an output only when an input is large enough to move the one-way clutch input side to engage with the next tooth or set of teeth of the one-way clutch output side. Accordingly, in a saw-toothed one-way clutch, tooth spacing angle determines the resolution. Conventionally, 72 teeth are used, which results in a resolution of 5 degrees. While an improved clutch with 90 teeth resulting in 4° resolution has been developed, a higher number of teeth appears impractical as far as ease of manufacture and tooth reliability are concerned.
U.S. Pat. No. 2,916,936 to Neracher, et al. discloses a transmission system with a synchronous blocker clutch having slidably engaging teeth. The engagement mechanism permits a certain amount of torque to be maintained from the engine to the transmission when shifting to provide a step up ratio. A blocker piece prevents the teeth from engaging until synchronization occurs.
U.S. Pat. No. 3,508,450 to Richards concerns a manual transmission with spring engaged forks used to decouple the input and output. The spring engaged forks allow slipping in case of torque mismatch.
U.S. Pat. No. 3,820,635 to Hurt relates to a mechanical actuator for a disc brake caliper. A ball and ramp arrangement is used to move a piston with teeth on one end into engagement with receiving portion teeth on the brake portion.
U.S. Pat. No. 4,380,276 to Sweet, et al. discloses a vehicle brake slack adjuster having saw-teeth of a drive ratchet engagable with saw-teeth of a coupling.
U.S. Pat. No. 4,621,714 to Skurka concerns a slack adjuster with a pair of clutch mechanisms that have cooperating teeth. The receiving portion has teeth spaced radially inward in order to provide finer increments of adjustment during application and release.
U.S. Patent Application Publication 2010/0018812 A1 to Louis relates to a slack adjuster with a one-way clutch having movable pawls. The arrangement of the clutch within the body allows for a clutch with a larger number of teeth and thereby finer adjustment.
International Publication WO 2005/098259 A1 to Echambadi, et al. discloses an automatic brake adjuster including a serrated worm shaft portion movable into and out of engagement with a one way lock/clutch seat serration for clutch regulation.